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bgkatz / 3phase_integrated

3-phase motor controller with integrated position sensor
MIT License
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Power consumption at no load and no speed #8

Open ekrimsk opened 2 years ago

ekrimsk commented 2 years ago

Hi Ben, Thanks for open sourcing all of this and providing nice documentation. I'm using one of the knock-offs from your design (T-motor AK80-6) and am trying to understand the power consumption I'm seeing. The module runs on 24V and when the motor isn't in control mode it consumes 28 mA.

When entering control mode, the current jumps up to ~110 mA (measured from benchtop supply). I'm trying to understand where this current is going. The DRV8323 should only consume ~12 mA and with the q-axis and d-axis currents set to zero (using kp =0, kd =0, tau_ff = 0, I_FW_MAX = 0) I would think the only other current would be for gate charge. Did you see similar current values on your mini-cheetah modules?

Thanks for the help!

bgkatz commented 2 years ago

That sounds a too high to me. I just checked one of my drives, and I see 30 mA idle at 24V, and 60 mA with the drive enabled and all commands set to zero. Maybe check how high the current bandwidth is set, and see if reducing it changes power consumption? If the current sensors on that variant of the drive are noisy, they'll introduce some extra current ripple, which could explain the higher power consumption. I expect you'd notice some very audible hissing noises if this were the case though.

The additional power when the drive is enabled should mostly be charging/discharging the FET gates and charging/discharging the FET output capacitance

ekrimsk commented 2 years ago

Thanks for the reply. The motor was very audible at the default current bandwidth. For some reason the current bandwidth doesn't show up in the settings menu for this version, but it appears to accept the commands (e.g. 'b200'). Reducing the current bandwidth significantly reduced the audible noise of the motor but the current consumption is still around 100 mA at no load and no speed.

How much current should I expect for the charge pump for the high side FETs at no load?

Does the load on the buck regulator change significantly when the motor is enabled and could this explain the power consumption? I'm wondering if I could reduce the total power draw by cutting traces and supplying a separate 5V input.

Thanks again!